Stretch plastic film, commonly known as stretch wrap, has gained substantial acceptance for such uses as warehouse packaging applications where plastic film is stretched around pallets, containers or irregular loads and allowing the built-in elastic recovery properties of the film to constrain the surrounded item(s). A number of plastic materials, such as PVC, LLDPE, LDPE and PE copolymerized with other suitable compounds such as vinyl acetate, acrylic acid or methacrylic acid, are used to produce stretch film for commercial use, with the usual thickness of such film being from about 18 to 30 microns.
The properties of the stretch film obtained are dependent upon a large number of variables, such as the extrusion process, film thickness, monolayer or co-extruded multilayer film, cooling rate, blow up ratio and stretch ratio. Currently, extensive research work is being carried out in industrial laboratories to improve the properties of stretch film, such as balance of peel/lap cling, tensile strength, tear resistance, transparency, etc.
Most stretch films are produced by a cast film process. However, a cast film process has inherent disadvantages in the production of stretch film. In the cast film process, orientation is effective only in the machine direction with consequent weakness in tensile strength. Also, due to inherent nature of the cast film process, edge trimming is essential. This usually results in kinks in the edges, thereby rendering the film vulnerable to tear. Tensile strength and tear properties can be improved by using a blown film process rather than a cast film process.
It is therefore an object of the invention to provide a suitable method for producing a stretch film by means of a blown film process.